The present invention concerns window structures for controlling the transmission of solar energy in general and, in particular, to window assemblies for selectively varying the transmission of light in the visible spectrum while selectively blocking solar radiation outside the visible spectrum.
Two methods, or some combination thereof, are generally utilized to reduce the transmission of solar energy through glass. The first method is absorption wherein the solar energy outside a particular band width is absorbed by predetermined elements in the glass and reradiated as heat. For example, U.S. Pat. No. 2,860,059 discloses a light absorbing glass suitable for automotive and architectural glazing applications. In a laminated automotive windshield in which two sheets of glass are bonded to an intermediate layer of polyvinyl butyral resin, the plastic layer is provided with a colored band extending across the upper portion of the windshield which band gradually decreases in light transmittance to provide a build-in glare screen for the windshield. An ultra-violet light absorbing glass is provided at least for the outer glass sheet to protect the colored band from fading in other injurious effects of the sun. The glass is ordinary soda-line-silica glass to which ultra-violet cut-off material such as ceric oxide and titanium dioxide combined with ferric oxide are added.
The other method of reducing the solar transmission is reflection. A reflecting material such as chromium is coated directly on the surface of the glass or onto the surface of a plastic sheet which is then adhered to the glass.
One of the problems associated with solar absorbing and solar reflecting window assemblies is that while a reduction in solar heating may be desirable during the summer, an increase in solar heating may be desirable during the winter. Therefore, many prior art devices have dealt with the problem of varying the solar transmission through a window assembly. For example, U.S. Pat. No. 3,056,626 discloses a device in which a flexible transparent screen of plastic sheet material is mounted between a pair of rollers located above and below an automobile windshield. A pair of spaced apart transparent plastic sheets are provided for guiding the flexible sheet during movement with respect to the windshield. The flexible sheet is provided with portions having different light transmissive or light filtering characteristics to provide for selective variation of solar transmission.
A moveable transparent or non-transparent shade can also be located in a window assembly between two fixed panes of glass such as shown in U.S. Pat. Nos. 4,281,488; 4,347,835; 4,382,436; and 4,508,154. U.S. Pat. No. 4,290,473 discloses a device for controlling light transmission in which a pair of spaced planar parallel films are placed adjacent a window opening and are moveable relative to one another. The films have uniformly and linearly varying light transmitting characteristics and are moved generally in opposite directions so that a substantially uniform degree of light transmission is achieved over the entire opening area. U.S. Pat. No. 4,520,611 discloses a double pane window having a flexible film disposed between the two panes and a member for stretching the flexible film taut.
Multipane or multi-glazed window assemblies have become an important element in reducing energy losses in buildings. However, as the number of panes increases, so does the weight of the assembly. Therefore, a window assembly having a flexible film in place of an intermediate pane of glass provides the advantage of reduced weight.